Communication method and system



Oct. 30, 1945. cV w. HANsELL COMMUNICATION METHOD AND SYSTEM Filed June 26,` 1942 INVENTOR (24PM/cf l1( A44/vnu.

`ATTORNEY Patented Oct. 30, 1945 f COMMUNICATION METHOD AND SYSTEM Clarence W.`Hansell, Port` Jefferson, N. Y., asl poration `of Delaware signorV to Radio Corporation of America, a cori; Application June 26, 1942, serial No. 448,579

10 Claims.

In this application I disclose a new and improved method of and means for signalling at radio frequency, high frequency and ultra-high frequency.,l u L i As. ls knownpthezquality of a .received signal atwA' 'and' B, Figure 1, isdetenmined bythe con- `ditins" of"operation, the frequency spectrum which may be entirely unacceptable in `telephony `lili:4

(Cl. 250f6) systems might be acceptable in telegraphy systems. Therefore, in a telegraphy system attenuation of the carrier relative to the sidebands is less harmful than in telephony systems. It

5 has been found thata small separation of two depends largely onthe carrier amplitudeand if waves of the order of10,000 to `20,000- cycles is the same is `reduced relative to the sideband or suicientto reduce greatlythe prob-ability 0f both sldebandsduring `transmission dueto fading or waves fading out to a, point at which distortion other causes, distortion at the `receiver results. results simultaneously. MOI'BGVGI, at 'the 1re# Furthermore, as is known, two carriers separated 10 ceiver selective circuits can readily separate curin the frequency spectrum have entirely different rents of frequencies differing by this amount and fading characteristics so that one may be received amplify the same. in,good strength when the other has faded out That the weaker .current from B modulates the and viceversa. l l phase of the stronger current from Awhen the` l I have provided anew and improved method l5 combined currents arepassed through a limiter and .means for communication wherein the will `be apparent to those skilled in the art by refbenets of frequency diversity are obtained along erence to Fig-ure 3. The weaker current from B with an improvement in operation eiiiciency. represented by vector 4 is added vectorially to the In describing my'` invention in detailreference stronger current from A represented by4 `vector e will -be `made to the attached drawing, wherein 20 6 at anglesvarying uniformly withrespect to time v Figure 1 illustrates diagrammatically a transat a rate of `360" per cycle of beat between them. mittersystem arranged to carry out my method This means that the resultant, or combined curof. communication;` rents, represented by, vector 8 varies in both am- 2 illustrates a receiver arranged to make plitude and `phase with` respect to vthe stronger use of :and derive thefbenets from energy trans- 25 initialcurrent represented by Vector 6. It also mittedbymy system of Figurel; is seen that the resultant current represented by While Figure 3 is a vector diagram illustrating vector. 8is equivalent in frequency to the stronger the` manner inwhich thecarrierand sidebands initial current with bothamplitude and phase arepzderived forttransmission in a system of Figmodulation addedjdue to the weaker initial curj 'L z Y. l i l 1 1l 30 rent. The resultant current deviates in phase Imm'ysystem lprovide at A and B two carrier l through an angle .9, and modulated in `amwaves,` of the vdesired frequency separation and plitude. (disregarding losses, etc., in 'the system) feedhothoffthese Waves` into a common amplifierA through a range twice the amplitude of the weak- Y system atC. e, ,l er ofthe two currents. q v Y .Oneiof thezcarriers, Say, 'for example, the one 35 Theampliner and limiter in C, however, refrom. A. .has astrength considerably greaterthan l move all variations in strength of `the resultant the other carrier.` from 1B. A"2: 1 ratio of strength current rep-resented by vectors through a range iS Satisfactory in many Cases. The amplifier C l0, Figure 3, fbut leaves `al1 `variations in phase also includes a current amplitude limiterr to take thereof. VThe resultant current after elimination out all amplitude variations ofthe carriersfand 40 of .amplitude modulation is a phase modulated VfliaiiiOnSqdue to combining thecarriers. Atthe l current which may be represented' or built up output of Clderive a phase modulated wave havfrom steady state sinuosoidal currents corre ing aalrel, the frequency. which CQI'IGSDOndS spending approximately to a carrier and two side to` thefrequeny of the lstronserfcrrier, that is, freqeun'cies. Consequently, a weaker initia1 eurt thftoll` derivedat Aand'two principal side fre- 45 rent can be made to phase modulate a stronger quenCieS 011` Oppositeisides vof `the first carrier initial ourrent'by combining the two and passing spaced. from` the said first carrier by the frequency them through an' amplitude limiten difference of the original carriers. l Assume, for example, that of the original car- The frequencyseparationof the two'carriers 50 riers, that supplied by A of Figure 1 is a strong Acarrier `of 15,000,000 cycles per second and that supplied ,by Bis a weaker carrier of of 14,990,000 cycles per second. When these two carriers are .combined and limited to constant amplitude, the result is a new phase modulated wave having a carrier of 15,000,000 `cycles and side frequencies y amplitude .of the stronger current.

In other words, "if the. carrieru'fromvA stronger carrier and is of 4frequency fs, while the carrier from B islthe weaker carrier and of fre. quency fw at the amplier-limiter stage in C, we will have a combined wave suclrthat from the, ,A output of C we may derive threemain frequencies,

sideband, fs corresponding to a newcarier, and js-(Jfs-'fzw corresponding to aylower sideband.

If the weaker of the originali carriers: hasan\. amplitude of one-half the amplitude (fof nthe .4 stronger original carrier then, after combining '20 and' limiting, the 'strngthlofneach of the two side' frequencies of the new'phase modulatedw'ave will be onequarter` thatoftthecarrier. AInfother Words, combiningfandlimiting two unequal carlriers substantially splits the relative'energy of the weakerofthe two carrier'siinto two parts of half i the original'relative amplitude, one at the original frequencyv and one symmetrically spaced in frequency 'with respect to the stronger of the original carriers.- :Toobtain practically undistorted phase modulation of the stronger carrierbythe weakerA carrier, the ratio of the two original carrier amplitudes should'never be Vallowedwto becomeY less tha'nl2t1 under anyconditions of modulation. Y

By lIr'iodulatingthe weaker of the-two:currents, that'is, theone derived from Bin Figure l, I produceeutof C ythefequiyalent -of twonew carriers bothmodul'atediin accordance with-,the signals and? "symmetrically spaced with respecty to the original carrier of the stronger frequency. These 4l twnew' carriers may thenvbe supplied tothe amplifiers and frequency multipliers in'D amplified to desired extent and multiplied in frequency and transmitted. Frequency multiplication I of the combined and amplitude limited `currents in.` crasesfthe phasedeviation ofthe new frequency multiplied current and'allowsfa=` larger ratio'of lthe l amplitudesfoi =thetwo initial currents to .be used; Y nt'the receiver, the-transmitted lwavestare; picked up andsu'pplie'd'throughselectivezfcircuit 50 andamplierE,'thefunction of which isftol pass. and amplify the transmitted wavesbutxtofreject. j

other waves not'in the `same-'frequency bandj The weaker carrierat B of Figure lmayfbe modulated amplitude'jin'phase or in frequency, 70.

provided theidetectors Mend N of Figure` 2`are" designed to demodul'ate theV corresponding typeJ ofY modulation. AIn anyfcasehashas been illuzsm, trained. in Figure. 3 tievel- -ffl'wll Hid* A' late. .the pbase grthestrqeee?. currents@ @uitleg s accepts S13-1.2.5. :vf

two new carriers sideband-like related to th stronger current will be modulated in amplitude, in phase, or in frequency in accordance with the modulations on theA weaker current.

Under the conditions described the strongest original carrier will contain a considerable part of the total transmitter power after combination and limiting. v,Plots/ever, py, adjusting the relative Strengths'vftheftw@ carrier @generateur m111- tiplying the frequency of theV combined and limited vvave a selected amount, the energy at the strongest original carrier frequency, in the final output Ifr'onithe.-transmittenfmay be reduced to any dedown to zero. The manner in "may be controlled in amplitude g h'e.degree of its phase modulation has' 'been deeib'idetail in my U. s. Patent No.

In practice it is preferable to use a rather large ratio Yof 'amplitudes of the two carrier currents in the transmitter. andstoiuse a' ratherlarge ratio '.of frequency multiplicationrof the; ccmbined andY .f limited currents.; :,.gf'f-'l e It is, of course, necessary that the frequency all,

the -str'onger fcurrent be `equal tothe desired mean ofj'allthe componentfrequency currents', isrcon stant and the transmitterv may operate.:;atf-ffull;,. class C-, 'highfeciency\output.j;' L t I Also, if desired,the modulations .of` the carrier' wave maygbefutilize'd asvathird communication channel-which is amplitudemodulatedfoppositely'f:v tothe' two siderfrequency.channelsl'j` Thatris'if the weaker of the two originalcarriers is .to;bei amplitude modulated by the SignaLQthermthel., modulation of .thesidelfrequencies andithe anodin lationy of vthe I carriera Wi-11.-be.opposite.:;to one iam other in such a mannerithat .theztota powe co r 1stant.=`

For..ultra-highgfrequencyi communlcationjovei'fshort.; distances the'..w.eakei= off .the .two: 'carriersei should preferably be frequency modulated vscedf'A in .this case,` frequency. modulationlisipreferableit amplitude or. :phaseimodulatiohzi nEor this typefofrli transmission -ia virtue; of .the systemiflsithatamtr 1l ference from another transmitter, produce'dieith 1 by accident '.-or by designi.sfisztunlikelyato j amnr block. Vboth channels simultaneouslylzand. commu I nicatiorr .is imoretlikelygto be :maintained in fsp'te ofeinterference:

I.C1a,im:...r .L.. e* 51. .In a ltransmission: system, faz-source Iof av energy of arst frequencyra'nd'a'given-amplitud f a source of signalv modulated; wave energy one ably less thanthe.` amplitude of-said1firstna` source,` a current `amplitude limiter` hai/ing input-coupled to both offr .said sour-ces; ancllfwavey transmitting., means. couple'dftothe outputo sai limiter- .lffel 3 im; :,:rl iii l.:

2,. acommunication system;y asourcaof wave energy of. .aiirstffrequency and a given ax'nplitudegi` a jsecond sourcewofymodulated waverenergygo Second. frequency and. of@A ani. amplitude lesstllamffY waarneemt sisealtrammiuinameenscoupled.;

to said output, and a receiver having a plurality of frequency selecting and demodulating means. and means for combining the outputs of said demodulating means.

3. In a transmission system, a source of wave energy of a rst frequency and a given amplitude,

. a source of signal modulated wave energy of a second frequency and of an amplitude considerably less than the amplitude of said first named source, a current amplitude limiter and frequency multiplier having an input coupled to both of said sources, and wave transmitting means coupled to the output of said limiter and frequency multiplier.

4. In a communication system, a source of wave` rality of selective means and signal detecting means responsive to said transmitted energy and means for combining the outputs of said detecting means.

5. In a transmission system, a source of wave energy of a first frequency and a given amplitude, a second source of signalmodulated wave energy of a second frequency and of an amplitude conslderably less than said given amplitude, a current amplitude limiter having an input coupled to said sources and having an output wherein appears wave energy including a carrier of said first frequency and side frequencies comprising modulated carriers on opposite sides of said first carrier and spaced therefrom by the difference between said first and second frequencies, and signal transmitting means coupled to said output.

6. A system as recited in claim wherein a frequency multiplier is included in the coupling between said current amplitude limiter and said transmitting means.

7. In a transmission system, a source of wave energy of a lirst frequency and a given amplitude, a second source of modulated wave energy of a second frequency and of an amplitude about onehalf of said given. amplitude, a current amplitude limiter having an input coupled to said sources and having an output wherein appears wave energy including a carrier of said first frequency and side frequencies comprising modulated carriers on opposite sides of said first carrier and and spaced therefrom by the difference between said rst and second frequencies, and signal transmitting means coupled to said output.

8. A system as recited in claim 7 wherein a frequency multiplier is included in said coupling between said current amplitude limiter and said f transmitting means.

9. In a transmission system, a source of wave energy of a first frequency and a given amplitude, a source of wave energy of a second frequency the timing of which is modulated in accordance with signals, said second mentioned Wave energy being of an amplitude considerably less than the amplitude of the wave energy of said first frequency, a current amplitude limiter having an input coupled to both of said sources, said current limiter having an output wherein appears wave energy including a first carrier of said first frequency and side frequencies comprising timing modulated carriers spaced from said first carrier by the difference between said first and second frequencies, and wave transmitting means coupled to the output of said current limiter.

10. A receiver for wave energy sent out by the system of claim 9 including an amplifier for all of said components of said limiter output, a frequency converter coupled to said amplifier, selec- 

